Light-emitting element including a charge injection transport layer having a recess portion for accumulating ink, and display device and method for manufacturing thereof

ABSTRACT

A light emitter and method for manufacturing a light emitter. The light emitter includes a first electrode, a charge injection transport layer, a light-emitting layer, and a second electrode that are layered in this order. At least the light-emitting layer is defined by bank. The charge injection transport layer includes a recessed portion having an inner bottom surface in contact with a bottom surface of the light-emitting layer and an inner side surface continuous with the inner bottom surface and in contact at least partly with a side surface of the light-emitting layer. The inner side surface has a lower edge continuous with the inner bottom surface, and an upper edge is aligned with a portion of a bottom periphery of the bank, the portion being in contact with the light-emitting layer or in contact with a bottom surface of the bank.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of PCT Application No.PCT/JP2010/000781 filed Feb. 9, 2010, and claims the benefit of priorityfrom Japanese Patent Application No. 2009-028971, filed Feb. 10, 2009,designating the United States of America, the disclosure of which,including the specification, drawings and claims, is incorporated hereinby reference in its entirety.

1. FIELD OF THE INVENTION

The present invention relates to a light emitter, a display apparatusand a method of manufacturing the light emitter, and in particular to anorganic EL element used in a display apparatus such as a flat displayapparatus.

2. DESCRIPTION OF RELATED ART

Conventionally, in a manufacturing process of an organic EL element,patterning by an ink-jet method is used to form a light-emitting layer.The ink-jet method is suitable for forming a uniform thin film patternin a micro area. The ink-jet method forms the uniform thin film patternat a pixel region defined by a bank by ejecting drops of an inkcomposition (hereinafter, referred to simply as “ink”) containing anorganic EL material into the pixel region and drying the ink.

When the above method is employed, a surface of the bank is subjectedto, for example, a liquid-repellent treatment using fluorine plasma. Asa result, the surface of the bank has low wettability to the ink and theejected ink becomes less likely to overflow the bank and flow in anadjacent pixel region. Accordingly, high-definition patterning becomespossible.

Moreover, Patent Literature 1 discloses a technology for patterning ahigher-definition light-emitting layer by: having a two-layered bankcomposed of a upper bank layer made of a liquid-repellent material and alower bank layer made of a liquid-philic material; making the upper banklayer have low wettability to the ink so that the ink is less likely tooverflow the bank; and making the lower bank layer have high wettabilityto the ink so that the ink easily stays in the pixel region.

3. PATENT LITERATURE Patent Literature 1

Japanese Patent Application Publication No. 2003-249375

SUMMARY OF INVENTION

However, in order to have the two-layered bank, manufacturing cost ofthe organic EL element increases since the number of processes increasescompared with having a single-layered bank.

In view of the above problem, the present invention aims to provide alight emitter on which a high definition light-emitting layer ispatterned and which can be manufactured at a low price.

A light emitter pertaining to an embodiment of the present invention isa light emitter including a first electrode, a charge injectiontransport layer, a light-emitting layer, and a second electrode that arelayered in this order, at least the light-emitting layer being definedby a bank, wherein the charge injection transport layer includes arecessed portion having (i) an inner bottom surface that is in contactwith a bottom surface of the light-emitting layer and (ii) an inner sidesurface that is continuous with the inner bottom surface and in contactat least with a part of a side surface of the light-emitting layer, andthe inner side surface of the recessed portion has a lower edge and anupper edge, the lower edge being continuous with the inner bottomsurface, the upper edge being one of (i) aligned with a part of a bottomperiphery of the bank, the part being in contact with the light-emittinglayer, and (ii) in contact with a bottom surface of the bank.

The light emitter pertaining to the embodiment of the present inventionincludes a charge injection transport layer including a recessed portionhaving an inner bottom surface that is in contact with a bottom surfaceof the light-emitting layer and an inner side surface that is continuouswith the inner bottom surface. Accordingly, in a manufacturing process,the recessed portion can accumulate drops of ink that have been ejectedin a region defined by a bank. In addition, on an inner surface of therecessed portion, the charge injection transport layer is principallycomposed of a metal compound that is more liquid-philic than the surfaceof the bank and has high wettability to the ink. Accordingly, the innersurface of the recessed portion can stably hold the drops of the inktherein. Therefore, the drops of the ink do not easily overflow the bankand flow in an adjacent pixel region, and a high definitionlight-emitting layer can be patterned. Additionally, the recessedportion can be easily formed by, for example, melting a part of thecharge injection transport layer with pure water. Also, unlike a lightemitter of Patent Literature 1, a complicated process for making atwo-layer bank is unnecessary. As a result, it is possible to enablesuch a light emitter at a low price.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing a layered condition of layersconstituting a light emitter pertaining to a first embodiment;

FIG. 2 is an enlarged view of a part enclosed with a dashed line in FIG.1;

FIGS. 3A-3D are schematic views for explaining a form of a recessedportion;

FIG. 4 is an enlarged view of a part enclosed with a dashed line in FIG.1, with respect to a light emitter pertaining to a modification;

FIGS. 5A-5D are schematic views for explaining the form of the recessedportion;

FIGS. 6A and 6B are schematic views for explaining a best thickness of alight-emitting layer;

FIG. 7 is an enlarged view of the part enclosed with the dashed line inFIG. 1, with respect to the light emitter pertaining to themodification;

FIGS. 8A-8D are processing drawings for explaining a method ofmanufacturing the light emitter pertaining to the first embodiment;

FIGS. 9E-9H are processing drawings for explaining the method ofmanufacturing the light emitter pertaining to the first embodiment,which follows FIG. 8D;

FIG. 10 is a schematic view showing a layered condition of layersconstituting a light emitter pertaining to a second embodiment;

FIGS. 11A-11D are processing drawings for explaining a method ofmanufacturing the light emitter pertaining to the second embodiment;

FIG. 12 is a schematic view showing a layered condition of layersconstituting a light emitter pertaining to a third embodiment;

FIGS. 13A-13D are processing drawings for explaining a method ofmanufacturing the light emitter pertaining to the third embodiment; and

FIG. 14 is a perspective view showing apparatuses such as a displayapparatus pertaining to a fourth embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[Embodiments]

A light emitter pertaining to an embodiment of the present invention isa light emitter including a first electrode, a charge injectiontransport layer, a light-emitting layer, and a second electrode that arelayered in this order, at least the light-emitting layer being definedby a bank, wherein the charge injection transport layer includes arecessed portion having (i) an inner bottom surface that is in contactwith a bottom surface of the light-emitting layer and (ii) an inner sidesurface that is continuous with the inner bottom surface and in contactat least with a part of a side surface of the light-emitting layer, andthe inner side surface of the recessed portion has a lower edge and anupper edge, the lower edge being continuous with the inner bottomsurface, the upper edge being one of (i) aligned with a part of a bottomperiphery of the bank, the part being in contact with the light-emittinglayer, and (ii) in contact with a bottom surface of the bank.

Here, a term “charge injection transport layer” is a collective term forlayers such as a hole injection layer, a hole transport layer, a holeinjection and transport layer, an electron injection layer, an electrontransport layer and an electron injection and transport layer. Forexample, the charge injection transport layer may be composed of thehole injection layer, the hole transport layer, two layers composed ofthe hole injection layer and the hole transport layer, the holeinjection and transport layer, the electron injection layer, theelectron transport layer, two layers composed of the electron injectionlayer and electron transport layer, and an electron injection transportlayer.

Note that, terms “liquid-philic” and “liquid-repellent” are each used ina relative sense. As described above, a bank has liquid-repellency atleast on a surface thereof. On the other hand, when the charge injectiontransport layer is principally composed of a metal compound withliquid-philicity, a surface of the charge injection transport layer ismore liquid-philic than the surface of the bank, and the surface of thebank is more liquid-repellent than the surface of the charge injectiontransport layer. Also, the surface of the charge injection transportlayer with liquid-philicity relatively has high wettability to ink, andthe surface of the bank with liquid-repellency relatively has lowwettability to the ink. Note that, liquid-philicity or liquid-repellencycan be, for example, defined by a contact angle at which the ink meetsthe surface of the bank or the charge injection transport layer. Forexample, when the contact angle is equal to or smaller than 10°, thesurface is defined to have liquid-philicity, and when the contactsurface is equal to or greater than 35°, the surface is defined to haveliquid-repellency.

Also, according to a specific aspect of the light emitter the chargeinjection transport layer is liquid-philic, and the bank isliquid-repellent.

Also, according to a specific aspect of the light emitter, the chargeinjection transport layer includes a metal compound that is soluble in apredetermined solvent, and the recessed portion is a portion of thecharge injection transport layer where the metal compound has beendissolved by the predetermined solvent.

Also, according to a specific aspect of the light emitter, thepredetermined solvent is one or both of (i) a developing solution forremoving a part of a resist film used to form the bank and (ii) acleaning liquid for cleaning residuals of the resist film that areremaining after the formation of the bank.

Also, according to a specific aspect of the light emitter, the chargeinjection transport layer is a hole injection layer including a metaloxide.

Also, according to a specific aspect of the light emitter, the metaloxide is an oxide of one of tungsten and molybdenum.

A display apparatus pertaining to the embodiment of the presentinvention includes any of the above light emitters.

A manufacturing method of the light emitter pertaining to the embodimentof the present invention comprises: a first step of forming a firstelectrode on a substrate; a second step of forming, above the firstelectrode, a thin film including a metal compound that is soluble in apredetermined solvent; a third step of forming a bank on the thin filmby (i) forming a resist film including a resist material on the thinfilm and (ii) etching the resist film with a developing solution; afourth step of, after the formation of the bank, forming a chargeinjection transport layer by cleaning residuals of the resist film thatadhere to the thin film with a cleaning liquid and dissolving a part ofthe thin film with the cleaning liquid, the charge injection transportlayer including a recessed portion having (i) an inner bottom surfaceand (ii) an inner side surface that is continuous with the inner bottomsurface and in contact at least with a part of a side surface of thelight-emitting layer, the inner side surface of the recessed portionhaving a lower edge and an upper edge, the lower edge being continuouswith the inner bottom surface, the upper edge being one of (i) alignedwith a part of a bottom periphery of the bank, the part being in contactwith the light-emitting layer, and (ii) in contact with a bottom surfaceof the bank; a fifth step of forming a light-emitting layer by (i)coating the inner bottom surface and the inner side surface of thecharge injection transport layer with ink by ejecting drops of the inkinto a region defined by the bank and (ii) drying the ink; and a sixthstep of forming a second electrode above the light-emitting layer.

Also, a manufacturing method of a light emitter, comprises: a first stepof forming a first electrode on a substrate; a second step of forming,above the first electrode, a thin film including a metal compound thatis soluble in a predetermined solvent; a third step of forming a bank onthe thin film by (i) forming a resist film including a resist materialon the thin film and (ii) etching the resist film with a developingsolution, and of forming a charge injection transport layer by cleaningresiduals of the resist film that adhere to the thin film and dissolvinga part of the thin film with the developing liquid, the charge injectiontransport layer including a recessed portion having (i) an inner bottomsurface and (ii) an inner side surface that is continuous with the innerbottom surface and in contact at least with a part of a side surface ofthe light-emitting layer, the inner side surface of the recessed portionhaving a lower edge and an upper edge, the lower edge being continuouswith the inner bottom surface, the upper edge being one of (i) alignedwith a part of a bottom periphery of the bank, the part being in contactwith the light-emitting layer, and (ii) being in contact with a bottomsurface of the bank; a fourth step of forming a light-emitting layer by(i) coating the inner bottom surface and the inner side surface of thecharge injection transport layer with ink by ejecting drops of the inkinto a region defined by the bank and (ii) drying the ink; and a sixthstep of forming a second electrode above the light-emitting layer.

The following explains a light emitter, a display apparatus and a methodof manufacturing the light emitter with reference to the drawings. Notethat contraction scale of members shown in each drawing differs fromreal scale.

[First Embodiment]

<Schematic Structure of Light Emitter>

FIG. 1 is a schematic view showing a layered condition of layersconstituting a light emitter pertaining to a first embodiment, and FIG.2 is an enlarged view of a part enclosed with a dashed line in FIG. 1.

As FIG. 1 shows, the light emitter pertaining to the first embodiment isa top emission type organic EL element including RGB pixels that arearranged in a matrix or in line. Each pixel has a layer structure andeach layer is disposed on a substrate.

On a TFT substrate 1 (hereinafter, referred to simply as “substrate 1”),a first electrode 2, which is an anode, is formed together with otherfirst electrodes 2 in a matrix or in line. On the first electrode 2, anindium tin oxide (ITO) layer 3, and a hole injection layer 4 as thecharge injection transport layer are layered in this order. Note that,while the ITO layer 3 is layered only on the first electrode 2, the holeinjection layer 4 is formed not only above the first electrode 2 butalso across an entire upper surface of the substrate 1.

On the hole injection layer 4, a bank 5 that defines pixels is formed,and in a region defined by the bank 5, a light-emitting layer 6 isdisposed. Furthermore, on the light-emitting layer 6, an electroninjection layer 7, a second electrode 8, which is a cathode, and apassivation layer 9 are formed so as to be continuous with respectivelayers of an adjacent pixel, passing over the region defined by the bank5.

The region defined by the bank 5 has a multi-layer structure accordingto which the ITO layer 3, the hole injection layer 4, the light-emittinglayer 6 and the electron injection layer 7 are layered in this order.Such a layer structure constitutes a functional layer. Note that, thefunctional layer may include other layers such as the hole transportlayer or the electron transport layer.

<Constituent Components of Light Emitter>

The substrate 1 is formed with an insulating material such as sodaglass, nonfluorescent glass, phosphate glass, borate glass, quartz,acrylic resin, styrenic resin, polycarbonate resin, epoxy resin,polyethylene, polyester, silicone resin, alumina, etc.

The first electrode 2 is formed with Ag (silver). Note that the firstelectrode 2 may be formed with APC (alloy of silver, palladium, andcopper), ARA (alloy of silver, rubidium, and gold), MoCr (alloy ofmolybdenum and chromium), NiCr (alloy of nickel and chromium), etc. Inthe case of a top emission type light emitter, it is preferable that thefirst electrode 2 be formed with a light-reflective material.

The ITO layer 3 exists between the first electrode 2 and the holeinjection layer 4 and has a function of guaranteeing excellentbondability between the first electrode 2 and the hole injection layer4.

The hole injection layer 4 contains a metal compound soluble in apredetermined solvent. To be specific, the hole injection layer 4 isformed with WOx (tungsten oxide) or MoWOx (molybdenum tungsten oxide).Note that the hole injection layer 4 only has to be formed with a metalcompound that is more liquid-philic than a surface of the bank 5.Examples of a metal compound having liquid-philicity include a metaloxide, metal nitride, or metal oxynitride.

When the hole injection layer 4 is formed with a metal oxide, holes canbe easily injected, contributing to effective light emission byelectrons in the light-emitting layer 6, which allows for excellentlight-emitting characteristics to be obtained. Examples of a metal oxideinclude an oxide of chromium (Cr), molybdenum (Mo), tungsten (W),vanadium (V), niobium (Nb), tantalum (Ta), titanium (Ti), zircon (Zr),hafnium (Hf), scandium (Sc), yttrium (Y), thorium (Th), manganese (Mn),iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), nickel (Ni), copper(Cu), zinc (Zn), cadmium (Cd), aluminum (Al), gallium (Ga), indium (In),silicon (Si), germanium (Ge), stannum (Sn), lead (Pb), antimony (Sb),bismuth (Bi), and so-called rare earth from lanthanum (La) to lutetium(Lu). Especially, aluminum oxide (Al₂O₃), copper oxide (CuO) and siliconmonoxide (SiO) can contribute to a prolonged service life.

It is preferable that the metal compound be composed of a transitionmetal. The transition metal occupies a plurality of potential levelssince there are a plurality of oxidation numbers. This makes holeinjection easy and allows for reduction of driving voltage.

As FIG. 2 shows, the hole injection layer 4 extends along the bottomsurface of the bank 5 to an adjacent pixel. Also, a portion of thecharge injection transport layer 4 in a region defined by the bank 5 hasa recessed structure in which the portion of the charge injectiontransport layer 4 is lower than the bottom surface of the bank 5, andincludes a recessed portion 4 a (indicated with mesh hatching in FIG. 2)formed by being dissolved by a predetermined solvent. In addition, withregard to the hole injection layer 4, only a film thickness in theregion defined by the bank 5 is smaller than a film thickness in otherregions, and the film thickness in the other regions is entirely andsubstantially uniform. Since the hole injection layer 4 is formed by ametal compound having liquid-philicity, an inner surface 4 b of therecessed portion 4 a has excellent wettability to ink. Accordingly, thisallows for drops of the ink ejected into the region defined by the bank5 to easily adhere to the inner surface 4 b of the recessed portion 4 a,and the drops of the ink easily stay within the region defined by thebank 5.

Note that, the hole injection layer 4 only has to have a recessedstructure according to which the recessed portion 4 a is lower than aperipheral portion 5 a of the bottom surface of the bank 5, and does nothave to be lower than the entire bottom surface of the bank 5. In therecessed structure of the present embodiment, the recessed portion 4 ais lower than the peripheral portion 5 a of the bottom surface of thebank but not lower than a central part 5 b of the bottom surface of thebank. Alternatively, for example, by setting the central part 5 b ashigh as the bottom peripheral portion 5 a and planarizing the bottomsurface of the bank 5, as an alternate long and two short dashes line 5c shows in FIG. 2, it may be possible to have the recessed structureaccording to which the recessed portion 4 a is lower than the entirebottom surface of the bank 5.

The hole injection layer 4 has a recessed structure according to which aportion of the hole injection layer 4 is lower than and aligned with thebottom periphery 5 d of the bank. To be specific, an upper surface ofthe hole injection layer 4, which is defined by the bank 5, is sunkenfrom a level of the bottom periphery 5 d in a direction substantiallyvertical to the upper surface of the substrate 1. Like this, in the caseof the recessed structure according to which the portion of the holeinjection layer 4 is lower than and aligned with the bottom periphery 5d of the bank 5, a film thickness of the light-emitting layer 6 can beuniformed over a wide range, and as a result, irregular luminance is notlikely to occur in the light-emitting layer 6.

The recessed structure of the hole injection layer 4 has a cup-likeshape. To be more specific, an inner surface 4 b of the recessed portion4 a is composed of an inner bottom surface 4 c and an inner side surface4 d. The inner bottom surface 4 c is substantially parallel with theupper surface of the substrate 1 and uniformed, and is in contact with abottom surface 6 a of the light-emitting layer 6. The inner side surface4 d extends from a periphery of the inner bottom surface 4 c in adirection perpendicular to the upper surface of the substrate 1 and isin contact with a side surface 6 b of the light-emitting layer 6. Whenthe recessed structure has a cup-like shape, the inner side surface 4 dprevents the drops of the ink within the recessed portion 4 a frommoving in a direction parallel to the upper surface of the substrate 1.Accordingly, it is possible to more stably hold the drops of the inkwithin the region defined by the bank 5. Moreover, when the recessedstructure has the cup-like shape, the inner surface 4 b of the recessedportion 4 a becomes larger in area, and a contact surface of the dropsof the ink and the hole injection layer 4 becomes larger in area.Accordingly, it is possible to more stably hold the drops of the inkwithin the region defined by the bank 5. Therefore, high-definitionpatterning of the light-emitting layer 6 is possible.

As described above, in the present embodiment, the bank 5 and the holeinjection layer 4 are connected to each other in a substantiallyvertical direction, and then the ink easily gets wet at a bottom of thelight-emitting layer 6. Accordingly, the light-emitting layer 6 withexcellent efficiency can be formed. Here, when the bank 5 and the holeinjection layer 4 are connected to each other in a horizontal direction,the ink do not easily get wet in the vicinity of a connection section ofthe bank 5 with the hole injection layer 4. Accordingly, thelight-emitting layer 6 might not be fully formed at the bottom surfacethereof, and as a result, electrical leakage might occur. That is, atechnical meaning resides in that the bank 5 and the hole injectionlayer 4 are connected to each other not in the horizontal direction butin the substantially vertical direction in order to excellently form thelight-emitting layer 6.

Note that, in the case that the bank 5 and the hole injection layer 4are connected to each other in the substantially vertical direction, thedirection is not limited to the vertical direction but may be a diagonaldirection. In other word, the direction only has to be a directionsubstantially perpendicular to the horizontal direction.

The following explains the recessed structure of the hole injectionlayer 4 in more detail. As FIG. 3A shows, the inner side surface 4 d ofthe recessed portion 4 a is composed of an lower side edge that iscontinuous with the inner bottom surface 4 c and an upper side edge 4 e(hereinafter, referred to as “upper edge 4 e”) that is continuous withthe lower side edge. The upper edge 4 e of the inner side surface 4 d ofthe recessed portion 4 a is aligned with a part of the bottom periphery5 d of the bank 5, the part of being in contact with the light-emittinglayer 6, and the inner side surface 4 d and the inner bottom surface 4 care continuous with each other in an R shape. Note that, when the upperedge 4 e of the inner side surface 4 d is aligned with the bottomperiphery 5 d of the bank 5, the recessed portion 4 a is not limited tothe shape shown in FIG. 3A, in which the inner side surface 4 d issubstantially vertical to the inner bottom surface 4 c. As FIG. 3Bshows, the inner side surface 4 d and a side surface 5 e of the bank 5may have substantially the same inclination and extend on the sameplane. As FIG. 3C shows, the inner side surface 4 d and the inner bottomsurface 4 c may be continuous with each other not in the R shape. AsFIG. 3D shows, the inner side surface 4 d may be inclined opposite tothe side surface 5 e of the bank 5 so as to go under the bank 5.

Alternatively, the hole injection layer 4 is not limited to have therecessed structure according to which the hole injection layer 4 islower than and aligned with the bottom periphery 5 d of the bank 5. Forexample, as FIG. 4 shows, the upper edge 4 e of the inner side surface 4d may not be aligned with the bottom periphery 5 d of the bank 5, andthe upper edge 4 e may be closer to an adjacent pixel than the bottomperiphery 5 d is. In such a case, As FIG. 5A shows, the inner sidesurface 4 d of the recessed portion 4 a has the upper edge 4 e that isin contact with a bottom surface 5 a of the bank 5. Note that, when theupper edge 4 e of the inner side surface 4 d is in contact with thebottom surface 5 a of the bank 5, the recessed portion 4 a is notlimited to the shape shown in FIG. 5A, in which the inner side surface 4d is substantially vertical to the inner bottom surface 4 c. As FIG. 5Bshows, the inner side surface 4 d and a side surface 5 e of the bank 5may have a substantially same inclination. As FIG. 5C shows, the innerside surface 4 d and the inner bottom surface 4 c may be continuous witheach other not in the R shape. As FIG. 5D shows, the inner side surface4 d may be inclined opposite to the side surface 5 e of the bank 5 so asto go under the bank 5.

Since the inner side surface 4 d has the upper edge 4 e that is alignedwith the bottom periphery 5 d of the bank 5 or the upper edge 4 e is incontact with the bottom surface 5 a of the bank 5, a short circuit isnot likely to occur between the electrodes 2 and 8. Supposedly, as aline with alternate long and two short dashes 10 shows in FIG. 4, whenthe upper edge 4 e of the inner side surface 4 d is not aligned with thebottom periphery 5 d of the bank 5 and the upper edge 4 e is closer toan adjacent pixel than the bottom periphery 5 d is, a short circuitmight occur between the electrodes 2 and 8 via an exposed area 4 f thatis a part of an upper surface of the hole injection layer 4 and exposedfrom the bank 5. Especially, as described later, when an average filmthickness h of the light-emitting layer 6 is smaller or equal to anaverage depth t of the recessed portion 4 a, an uncovered area 4 f ofhole injection layer 4 that is a part of an upper surface of the holeinjection layer 4 and uncovered with the bank 5 might be in contact withthe electron injection layer 7 or the second electrode 8. Accordingly, ashort circuit might occur between the electrodes 2 and 8.

Returning to FIG. 2, though the invention of the present applicationdoes not specifically specify the average depth t of the recessedportion 4 a, the average depth t may be 5-100 nm, for example. If theaverage depth t of the recessed portion 4 a is equal to or greater than5 nm, it is possible to hold sufficient amount of the ink within therecessed portion 4 a. Accordingly, it is possible to stably maintain theink within the region defined by the bank 5. Furthermore, since thelight-emitting layer 6 is formed until a periphery of the bank 5 withoutbeing rejected, the short circuit between the electrodes 2 and 8 can beprevented.

Note that, the average depth t of the recessed portion 4 a can beobtained by measuring a surface profile of the hole injection layer 4with use of a stylus profiler meter or an AFM (Atomic Force Microscope),and calculating a difference between an average height of a portion thatis a crest and an average height of a portion that is a trough based onthe surface profile.

On the other hand, the film thickness of the light-emitting layer 6 isnot specifically determined. However, if an average film thickness h ofthe light-emitting layer 6 after dried is equal to or greater than 100nm and an average depth t of the recessed portion 4 a is equal to orsmaller than 100 nm, for example, it is possible to uniform a filmthickness of the light-emitting layer 6 at the region defined by thebank 5.

Furthermore, it is preferable that a difference between the average filmthickness h of the light-emitting layer 6 and the average depth t of therecessed portion 4 a be equal to or smaller than 20 nm. When the averagefilm thickness h of the light-emitting layer 6 is much smaller than theaverage depth t of the recessed portion 4 a (for example, t−h>20 nm),there is a portion that is out of contact with the light-emitting layer6 (portion not covered with the light-emitting layer 6) at the innerside surface 4 d of the recessed portion 4 a, as FIG. 6A shows. Then ashort circuit might occur between the electrodes 2 and 8 at thatportion. On the other hand, when the average film thickness h of thelight-emitting layer 6 is much greater than the average depth t of therecessed portion 4 a (for example, h−t>20 nm), liquid-repellency of thebank 5 causes a film thickness of a bank vicinity portion 6 c of thelight-emitting layer 6 to become smaller than other portions, as FIG. 6Bshows. As a result, a cross-sectional shape of the light-emitting layer6 has a substantially convex shape, and this might result in irregularlight emission caused by a difference of film thickness.

Note that, the inner side surface 4 d of the recessed portion 4 a onlyhas to be in contact with at least a part of the side surface 6 b of thelight-emitting layer 6. For example, as FIG. 2 and FIG. 6B show, whenthe average film thickness h of the light-emitting layer 6 is equal toor greater than the average depth t of the recessed portion 4 a, only apart of a lower part of the side surface 6 b of the light-emitting layer6 is in contact with the inner side surface 4 d of the recessed portion4 a. On the other hand, as FIG. 6A shows, when the average filmthickness h of the light-emitting layer 6 is smaller than the averagedepth t of the recessed portion 4 a, the side surface 6 b of thelight-emitting layer 6 is entirely in contact with the inner sidesurface 4 d of the recessed portion 4 a.

As FIG. 7 shows, in the recessed portion 4 a of the hole injection layer4, a liquid-philic layer 12 such as an IL layer (intermediate layer) maybe formed under the light-emitting layer 6. In this case, the drops ofthe ink are ejected not on the inner bottom surface 4 c of the recessedportion 4 a but on an upper surface 12 a of the liquid-philic layer 12.However, since the upper surface 12 a is liquid-philic, it is possibleto stably hold the drops of the ink within the region defined by thebank 5. However, if the recessed portion 4 a is totally filled with theliquid-philic layer 12, the inner side surface 4 d of the recessedportion 4 a becomes out of contact with the ink. Accordingly, an averagefilm thickness g of the liquid-philic layer 12 is preferably smallerthan the average depth t of the recessed portion 4 a.

The bank 5 is formed with an organic material such as resin or aninorganic material such as glass and has insulating properties. Examplesof the organic material include acrylic resin, polyimide resin,novolac-type phenolic resin, etc. Examples of the inorganic materialinclude silicon oxide (SiO₂), silicon nitride (Si₃N₄), etc. It ispreferable that the bank 5 have organic solvent resistance, and havecertain light transparency to visible light. Furthermore, since the bank5 is etched, baked, etc. when formed, it is preferable that the bank 5be formed from a material highly resistant to the etching and bakingprocesses.

At least the surface of the bank 5 is provided with liquid-repellency.Accordingly, when the bank 5 is formed with a liquid-philic material, itis necessary that the surface of the bank 5 be subjected to, forexample, a liquid-repellent treatment in order to make the surface ofthe bank 5 liquid-repellent.

Note that the bank 5 may be a pixel bank or a line bank. In the case ofa pixel bank, the bank 5 is formed to surround a whole circumference ofthe light-emitting layer 6 including a pixel. In the case of a linebank, the bank 5 is formed to define a plurality of pixels by column orby row. In other words, the bank 5 exists only as columns or as rows oneither side of a light-emitting layer 6, and a light-emitting layer 6 iscontinuous with other light-emitting layers 6 in the same column or row.

Specifically, it is preferable that the organic light-emitting layer 6be formed from a fluorescent material such as an oxinoid compound,perylene compound, coumarin compound, azacoumarin compound, oxazolecompound, oxadiazole compound, perinone compound, pyrrolo-pyrrolecompound, naphthalene compound, anthracene compound, fluorene compound,fluoranthene compound, tetracene compound, pyrene compound, coronenecompound, quinolone compound and azaquinolone compound, pyrazolinederivative and pyrazolone derivative, rhodamine compound, chrysenecompound, phenanthrene compound, cyclopentadiene compound, stilbenecompound, diphenylquinone compound, styryl compound, butadiene compound,dicyanomethylene pyran compound, dicyanomethylene thiopyran compound,fluorescein compound, pyrylium compound, thiapyrylium compound,selenapyrylium compound, telluropyrylium compound, aromatic aldadienecompound, oligophenylene compound, thioxanthene compound, anthracenecompound, cyanine compound, acridine compound, metal complex of a8-hydroxyquinoline compound, metal complex of a 2-bipyridine compound,complex of a Schiff base and a group three metal, metal complex ofoxine, rare earth metal complex, etc., as recited in Japanese UnexaminedPatent Application Publication No. H5-163488. When the light-emittinglayer 6 includes a layer formed with a high-polymer material, thelight-emitting layer 6 can be formed by a printing technology such as anink-jet method, and a nozzle coating method. Accordingly, compared witha deposition method using a low-molecular material, is it possible toeasily contribute to cost reduction.

The electron injection layer 7 has the function of transportingelectrons injected through the second electrode 8 to the light-emittinglayer 6 and is preferably formed, for example, from barium,phthalocyanine, lithium fluoride, or a combination thereof.

The second electrode 8 is formed from ITO, indium zinc oxide (IZO), etc.In the case of a top emission type light emitter, it is preferable thatthe first electrode 8 be formed with a light transparent material.

The passivation layer 9 has the function of controlling thelight-emitting layer 6 or other layers from being exposed to water orair and is formed, for example, from silicon nitride (SiN), siliconoxynitride (SiON), etc. In the case of a top emission type lightemitter, it is preferable that the passivation layer 9 be formed from alight transparent material.

<Method of Manufacturing Light Emitter>

FIGS. 8A-8D are processing drawings for explaining a method ofmanufacturing a light emitter pertaining to the first embodiment. FIGS.9E-9H are processing drawings for explaining the method of manufacturingthe light emitter pertaining to the first embodiment, which follows FIG.8D.

In the manufacturing process of a light emitter pertaining to the firstembodiment, first, as FIG. 8A shows, the first electrode 2 is formed onthe substrate 1 that is made of glass together with other firstelectrodes 2 in a matrix or in line, by forming a thin Ag film, forexample, by a sputtering method and then patterning the thin Ag film,for example, by photolithography. Note that the thin Ag film may beformed by vacuum deposition or the like.

Next, as FIG. 8B shows, a thin ITO film is formed by, for example,sputtering, and then the ITO layer 3 is formed by patterning the thinITO film by photolithography, for example.

Following this, the thin film 11 containing a metal compound soluble ina predetermined solvent is formed. For example, using a compoundcontaining WOx or MoWOx, the thin film 11 formed from WOx or MoWOx areformed by a vacuum deposition method or a sputtering method, to beuniform all over an upper surface of the substrate 1.

Next, as FIG. 8C shows, the bank 5 is formed, for example, byphotolithography, so as to surround each pixel region (region at whichthe first electrode 2 is positioned). In such a case, for example, aresist film (for example, resin film) including a resist material isformed on the thin film 11, for example, by coating, and a resistpattern is formed on the resist film. After that, a desired portion ofthe resist film is etched by applying a developing solution and removedto form patterning of the bank 5. Note that, when the bank 5 is formedfrom an inorganic material, the bank is formed by a CVD method, forexample. Residuals of the resist film that are attached on a surface ofthe thin film 11 after etching are removed by hydrofluoric acid, forexample. Furthermore, a liquid-repellent treatment is applied to thesurface of the bank 5, if necessary.

Next, as FIG. 8D shows, the hole injection layer 4 is formed by formingthe recessed portion 4 a by melting a part of the thin film 11. Thereby,in the hole injection layer 4, the region defined by the bank 5 has afilm thickness smaller than a film thickness of other areas. Therecessed portion 4 a is formed, for example, when an impure substancesuch as hydrofluoric acid remaining on the surface of the bank 5 isbeing cleaned with pure water after residuals of the resist film areremoved, by melting the region defined by the bank 5 on an upper surfaceof the thin film 11 with the pure water. In such a case, pure water isthe predetermined solvent, and it is possible to change a depth and ashape of the recessed portion 4 a by changing condition of cleaning withthe pure water.

As a specific method, for example, the substrate 1 is cleaned byejecting pure water (for example, of a room temperature) thereon, whilea spin coater keeps rotating the substrate 1. After that, while thesubstrate 1 is kept rotating, pure water is stopped being ejected andthen drained. In this case, it is possible to change the depth and theshape of the recessed portion 4 a by changing a time period for ejectingthe pure water. Since a melting speed of the thin film 11 also changesaccording to a temperature of pure water, it is also possible to adjustthe depth and the shape of the recessed portion 4 a by the temperatureof pure water.

A method for forming the recessed portion 4 a is not limited to theabove. For example, after the formation of the bank 5, while theresiduals of the resist film that are attached on the surface of thethin film 11 are being cleaned with a cleaning liquid such as purewater, the recessed portion 4 a may be formed by melting a part of thethin film 11 by the cleaning liquid at the same time. In such a case,the predetermined solvent is the cleaning liquid. Alternatively, whilethe resist film is being etched by the developing solution to form thebank 5 and the residuals of the resist film that are attached on thethin film 11 are being cleaned by the developing solution, the recessedportion 4 a may be formed by melting the part of the thin film 11 at thesame time. In such a case, the predetermined solvent is the developingsolution.

When the hole injection layer 4 is formed by dissolving the thin film 11with use of a solvent such as a cleaning liquid and a developingsolution that are used in forming the bank, productive efficiency ishigh since a different predetermined solvent to form the recessedportion 4 a is not required and an additional process to form therecessed portion 4 a is also not required.

Note that the recessed portion 4 a is not limited to be formed by usingthe predetermined solvent. Another method like the following may beused. For example, first, a thin film made of WOx or MoWOx is formedwith use of spattering and photolithography at all the area except anarea at which the first electrode 2 is located. After that, on the thinfilm, another thin film made of WOx or MoWOx is formed to cover all thearea and the hole injection layer 4 having a recessed shape is formed atthe area at which the first electrode 2 is located.

Next, as FIG. 9E shows, the light-emitting layer 6 is formed by ejectingdrops of the ink by, for example, the ink-jet method in the regiondefined by the bank 5, coating the ink along the inner bottom surface 4c and the inner side surface 4 d of the hole injection layer 4, anddrying the ink. Note that the ink may be ejected by other methods suchas a dispenser method, a nozzle coating method, a spin coat method, anintaglio printing, and a letterpress printing.

Next, as FIG. 9F shows, a thin barium film that will be the electroninjection layer 7 is formed by, for example, vacuum deposition. Then asFIG. 9G shows, an ITO thin film that will be the second electrode 8 isformed by, for example, spattering. After that, as FIG. 9H shows, thepassivation layer 9 is formed.

[Second Embodiment]

A light emitter pertaining to a second embodiment is greatly differentfrom the light emitter pertaining to the first embodiment in that theITO layer is not formed under the hole injection layer and that aprotection film is formed on the hole injection layer. The followingexplanation focuses on the difference from the first embodiment, andexplanation of the same structure as the first embodiment will besimplified or omitted.

<Structure of Light Emitter>

FIG. 10 is a schematic view showing a layered condition of layersconstituting a light emitter pertaining to a second embodiment. As FIG.10 shows, a light emitter pertaining to the second embodiment includes afirst electrode 102, which is an anode, formed on a substrate 101, and ahole injection layer 104 and a protective layer 110 are layered thereonin this order as a charge injection transport layer. Note that the holeinjection layer 104 is formed across an entire upper surface of thesubstrate 101, but the protective layer 110 is not formed above thefirst electrode 102. In addition, an ITO layer does not exist betweenthe first electrode 102 and the hole injection layer 104.

On the hole injection layer 104, a bank 105 for defining pixels isformed. A light-emitting layer 106 is layered in a region defined by thebank 105, and on the light-emitting layer 106, an electron injectionlayer 107, a second electrode 108, which is a cathode, and a passivationlayer 109 are formed so as to be continuous with respective layers of anadjacent pixel, passing over the region defined by the bank 105.

<Method of Manufacturing Light Emitter>

FIGS. 11A-11D are processing drawings for explaining a method ofmanufacturing a light emitter pertaining to the second embodiment. Inthe manufacturing process of the light emitter pertaining to the secondembodiment, as FIG. 11A shows, first, on the substrate 101 that is madeof glass, the first electrode 102 is formed with an aluminum-based (Al)material. Next, a thin film 111 made of WOx or MoWOx, which will be thehole injection layer 104 later, is formed on the first electrode 102.Then a thin film 112 made of WOx or MoWOx, which will be the protectivelayer 110, is formed on the thin film 111. The thin film 112 protectsthe hole injection layer 104 during etching for forming the bank 105.

Next, as FIG. 11B shows, the bank 105 is formed on the thin film 112. Tobe specific, a resist film including a resist material is formed on thethin film 112, and a resist pattern is formed on the film. After that adesired portion of the resist film is etched by applying a developingsolution and removed to form patterning of the bank 105. Note that animpure substance such as hydrofluoric acid remaining on a surface of thebank 105 after the formation of the bank is cleaned by a cleaning liquidsuch as pure water and removed, and a region defined by the bank 105 onan upper surface of the thin film 112 is melted by the cleaning liquidand becomes recessed.

Furthermore, as FIG. 11C shows, as the treatment with the cleaningliquid continues, the entire region defined by the bank 105 on the thinfilm 112 melts and accordingly the protective layer 110 is formed. Whenthe thin film 112 melts, the thin film 111 is exposed and the regiondefined by the bank 105 on the upper surface of the thin film 111 meltsand becomes recessed and then a recessed portion 104 a is formed. Thus,the hole injection layer 104 is formed.

Next, as FIG. 11D shows, the light-emitting layer 106 is formed withinthe region defined by the bank 105. Subsequent processes are the same asin Embodiment 1, and therefore a description thereof is omitted.

[Third Embodiment]

A light emitter pertaining to a third embodiment is greatly differentfrom the light emitter pertaining to the second embodiment in an area atwhich a hole injection layer is formed. The following explanationfocuses on the difference from the second embodiment, and explanation ofthe same structure as the second embodiment will be simplified oromitted.

<Structure of Light Emitter>

FIG. 12 is a schematic view showing a layered condition of layersconstituting a light emitter pertaining to the third embodiment. As FIG.12 shows, a light emitter pertaining to the third embodiment includes afirst electrode 202, which is an anode, formed on a substrate 201, and ahole injection layer 204 and a protective layer 210 are layered thereonin this order as a charge injection transport layer. Note that the holeinjection layer 204 is not formed across the entire upper surface of thesubstrate 1, but formed only on the first electrode 202 and at asurrounding area of the first electrode 202. On the other hand, theprotective layer 210 is not formed above the first electrode 202.

On the hole injection layer 204, a bank 205 for defining pixels isformed. A light-emitting layer 206 is layered in a region defined by thebank 205, and on the light-emitting layer 206, an electron injectionlayer 207, a second electrode 208, which is a cathode, and a passivationlayer 209 are formed so as to be continuous with respective layers of anadjacent pixel, passing over the region defined by the bank 205.

<Method of Manufacturing Light Emitter>

FIGS. 13A-13D are processing drawings for explaining a method ofmanufacturing a light emitter pertaining to the third embodiment. In themanufacturing process of the light emitter pertaining to the thirdembodiment, as FIG. 13A shows, first, on the substrate 101 that is madeof glass, the first electrode 102 is formed with an Al material. Next,an oxide film 211 that will be a hole injection layer 204 is formed byoxidizing an exposed surface (upper surface and side surface) of thefirst electrode 102. Then a thin film 212 made of WOx or MoWOx, whichwill be the protective layer 210 later, is formed on the oxide film 211.

Next, as FIG. 13B shows, the bank 205 is formed on the thin film 212. Animpure substance such as hydrofluoric acid remaining on a surface of thebank 205 is cleaned with a cleaning liquid such as pure water andremoved, and a region defined by the bank 205 on an upper surface of thethin film 212 is melted by the cleaning liquid and becomes recessed.

Furthermore, as FIG. 13C shows, as the treatment with the cleaningliquid continues, all the region of the thin film 212, which is definedby the bank 205, melts and accordingly a final form, that is, theprotective layer 210 is formed. In addition, when the thin film 212melts, the region defined by the bank 205 on the thin film 211 isexposed. Accordingly, the upper surface of the region also melts andbecomes recessed, and then the recessed portion 204 a is formed. Thus,the hole injection layer 204 is formed.

Next, as FIG. 13D shows, the light-emitting layer 206 is formed withinthe region defined by the bank 205. Subsequent processes are the same asin First Embodiment, and therefore a description thereof is omitted.

[Fourth Embodiment]

FIG. 14 is a perspective view showing apparatuses such as a displayapparatus pertaining to a fourth embodiment. As FIG. 14 shows, a displayapparatus 300 pertaining to an embodiment of the present invention is anorganic EL display formed by a plurality of pixels arranged in a matrix.Each pixel emits a color corresponding to one of R (red), G (green), orB (blue) and composed of a light emitter pertaining to the embodiment ofthe present invention.

[Modification]

As described above, the light emitter, the display apparatus and themanufacturing method of the light emitter pertaining to the presentembodiments have been explained. However, the light emitter, the displayapparatus and the manufacturing method of the light emitter pertainingto an embodiment of the present invention are not limited to the aboveembodiments.

For example, the charge injection transport layer is not limited to thehole injection layer, and may be the hole transport layer or holeinjection and transport layer. Also, the first electrode may be acathode, and the second electrode may be an anode. In such a case, thecharge injection transport layer may be the electron injection layer,the electron transport layer or the electron injection and transportlayer.

Also, the light emitter is not limited to the top-emission type, and maybe a bottom-emission type.

INDUSTRIAL APPLICABILITY

The present invention can be utilized for an organic EL displayapparatus used in an apparatus such as a plane light source and a platdisplay apparatus.

We claim:
 1. A light emitter, comprising: a first electrode; a chargeinjection transport layer; a light-emitting layer; and a secondelectrode, said first electrode, said charge injection transport layer,said light-emitting layer and said second electrode being layered inthis order, at least said light-emitting layer being defined by a bank,wherein said charge injection transport layer includes a recessedportion, said recessed portion including an inner bottom surface that isin contact with a bottom surface of said light-emitting layer and aninner side surface that is continuous with said inner bottom surface,said inner side surface being in contact at least with a part of a sidesurface of said light-emitting layer, said inner side surface of saidrecessed portion having a lower edge continuous with said inner bottomsurface, and an upper edge at least one of aligned with a portion of abottom periphery of said bank that contacts said light-emitting layer,and contacting a bottom surface of said bank.
 2. The light emitter ofclaim 1, wherein said charge injection transport layer is liquid-philicand said bank is liquid-repellent with respect to an ink compositioncontaining an organic EL material from which said light-emitting layeris formed.
 3. The light emitter of claim 1, wherein said chargeinjection transport layer includes a metal compound dissolvable by apredetermined solvent, said recessed portion comprising a portion ofsaid charge injection transport layer where said metal compound has beendissolved by the predetermined solvent.
 4. The light emitter of claim 3,wherein the predetermined solvent comprises at least one of a developingsolution for removing a part of a resist film used to form said bank anda cleaning fluid for cleaning residuals of the resist film that remainafter forming said bank.
 5. The light emitter of claim 1, wherein saidcharge injection transport layer comprises a hole injection layerincluding a metal oxide.
 6. The light emitter of claim 5, wherein saidmetal oxide comprises an oxide of one of tungsten and molybdenum.
 7. Adisplay apparatus, comprising said light emitter of claim
 1. 8. Thelight emitter of claim 1, wherein said recessed portion has an averagedepth of 5 nm to 100 nm.
 9. The light emitter of claim 1, wherein saidlight-emitting layer has an average film thickness that is smaller thanan average depth of said recessed portion.
 10. The light emitter ofclaim 1, wherein an inclination angle of said inner side surface of saidrecessed portion relative to said inner bottom surface is substantiallyequal to an inclination angle of said bank relative to said inner bottomsurface.
 11. The light emitter of claim 1, wherein an inclination angleof said inner side surface of said recessed portion relative to saidinner bottom surface is greater than an inclination angle of said bankrelative to said inner bottom surface.
 12. The light emitter of claim 1,wherein an inclination angle of said inner side surface of said recessedportion relative to said inner bottom surface is less than aninclination angle of said bank are substantially equal relative to saidinner bottom surface.
 13. The light emitter of claim 3, wherein a depthof said recessed portion is predetermined in accordance with a meltingspeed of said metal compound with respect to the predetermined solvent,the melting speed being based on a temperature of the predeterminedsolvent.
 14. A light emitter, comprising: a first electrode; a chargeinjection transport layer; an intermediate layer; a light-emittinglayer; and a second electrode, said first electrode, said chargeinjection transport layer, said intermediate layer, said light-emittinglayer and said second electrode being layered in this order, at leastsaid light-emitting layer being defined by a bank, wherein said chargeinjection transport layer includes a recessed portion, said recessedportion including an inner bottom surface that is in contact with abottom surface of said intermediate layer and an inner side surface thatis continuous with said inner bottom surface, said inner side surfacebeing in contact at least with a part of a side surface of saidintermediate layer, and said inner side surface of said recessed portionhaving a lower edge continuous with said inner bottom surface, and anupper edge at least one of aligned with a portion of a bottom peripheryof said bank that contacts said intermediate layer, and contacting abottom surface of said bank.
 15. The light emitter of claim 14, whereinsaid intermediate layer is liquid-philic with respect to an inkcomposition containing an organic EL material from which saidlight-emitting layer is formed.
 16. The light emitter of claim 14,wherein said light-emitting layer is in contact with said intermediatelayer.
 17. The light emitter of claim 14, wherein said intermediatelayer has an average film thickness that is smaller than an averagedepth of said recessed portion.
 18. The light emitter of claim 14,wherein said charge injection transport layer is liquid-philic and saidbank is liquid-repellent with respect to an ink composition containingan organic EL material from which said light-emitting layer is formed.19. The light emitter of claim 14, wherein said charge injectiontransport layer includes a metal compound dissolvable by a predeterminedsolvent, said recessed portion comprising a portion of said chargeinjection transport layer where said metal compound has been dissolvedby the predetermined solvent.
 20. The light emitter of claim 19, whereinthe predetermined solvent comprises at least one of a developingsolution for removing a part of a resist film used to form said bank anda cleaning fluid for cleaning residuals of the resist film that remainafter forming said bank.
 21. The light emitter of claim 19, wherein adepth of said recessed portion is predetermined in accordance with amelting speed of said metal compound with respect to the predeterminedsolvent, the melting speed being based on a temperature of thepredetermined solvent.
 22. The light emitter of claim 14, wherein saidcharge injection transport layer comprises a hole injection layerincluding a metal oxide.
 23. The light emitter of claim 22, wherein saidmetal oxide comprises an oxide of one of tungsten and molybdenum.
 24. Adisplay apparatus, comprising said light emitter of claim 14.